1. Field of the Invention
The present invention relates to an organic electroluminescent device and a driving method thereof. Particularly, the present invention relates to the organic electroluminescent device capable of changing a discharging level according to gray scale, and a driving method thereof.
2. Description of the Related Art
An organic electroluminescent device is a device emitting a light having a predetermined wavelength when a certain voltage is applied thereto.
FIG. 1 is a view showing an organic electroluminescent device in the art. And, FIG. 2 is a timing diagram showing scan signal and data current provided to pixels of FIG. 1.
In FIG. 1, the organic electroluminescent device in the art includes a panel 100, a scan driving circuit 110, a control circuit 120, a data driving circuit 130, a pre-charging circuit 140 and a discharging circuit 150.
The panel 100 includes a plurality of pixels E11 to E44 formed on an emitting area crossing over data lines D1 to D4 and scan lines S1 to S4.
The scan driving circuit 110 transmits scan signals to the pixels through the scan lines S1 to S4 in sequence.
The control circuit 120 receives a display data inputted from outside, for example, RGB data, and transmits a control signal to the scan driving circuit 110, the data driving circuit 130, the pre-charging driving circuit 140, and the discharging circuit 150 according to the display data.
Hereinafter, the driving method of the organic electroluminescent device will be described in detail.
But, for the convenience of explanation, it is assumed that a first display data and a second display data are inputted to the control circuit 120 in sequence.
The pre-charging circuit 140 applies a first pre-charge current according to the first display data provided from the control circuit 120 to the data lines D1 to D4 during a first pre-charge time pcha1 as shown in FIG. 2.
In this case, the first pre-charge current is sufficiently overshooting during the first pre-charge time pcha1 because the first display data is high gray scale (80%). Thus, the pixels E11 to E44 are emitting a light as the gray scale of 80% from the starting time T2 of a low logic area in the second scan signal SP2.
Then, the data driving circuit 130 provides a first data current (the gray scale of 80%) according to the first display data transmitted from the control circuit 120 to the pixels E11 to E44 through the data lines D1 to D4.
Subsequently, the discharging circuit 150 discharges the data lines D1 to D4 to a certain discharge level DL1 according to the first display data transmitted from the control circuit 120 during a second discharge time. The discharging circuit 150 is formed with a plurality of Zener diodes ZD1 to ZD4, and so the discharge level is uniformly fixed independently of the emitting gray scale of the pixels E11 to E44.
Next, the pre-charging circuit 140 applies a second pre-charge current according to the second display data provided from the control circuit 120 to the data lines D1 to D4 during a second pre-charge time pcha2.
Then, the data driving circuit 130 provides a second data current (the gray scale of 20%) according to the second display data transmitted from the control circuit 120 to the pixels E11 to E44 through the data lines D1 to D4.
In this case, the second pre-charge current is not sufficiently overshooting because the second display data is the low gray scale (20%). As a result, the pixels E11 to E44 emits as the gray scale of 20% after passing the starting time T3 of the low logic area in a third scan signal SP3, like the A area of FIG. 2
Thus, the pixels E11 to E44 could not emit a light with desired brightness.
In case a light is emitted in the low gray scale after the light is emitted in high gray scale as shown above, the pixels E11 to E44 could not emit a light with desired brightness, and the consumption power is increased to emit a light with desired brightness.